TECHNICAL issues, and assisted with their solutions. Following is a review of these experiences. What Is Happening? 1. Thermal expansion and contraction of the metal panels generate forces if resistance to this movement occurs. Any resistance forces generated need to be effectively handled, or alternatively the movement of the roof panels must be allowed. Roof panels can change in length significantly over their entire temperature exposure range. It is not uncommon for a steel roof panel to change in length at least ½” in 40’ of panel length from the coldest to the warmest temperature exposure. Roof panels of 100 percent aluminum move at approximately twice the rate of steel. 2. Tall, wide, and long post-frame structures can structurally tolerate more movement than conventional construction. This increased movement, however, can cause problems with building weathertightness. The post-frame structure resists the various loads as an assembled “unit.” It is important to note that even when the roof system is not used as a structural diaphragm by the building design professional in the building design, it is still part of the structure and will take load unless the framing below is stiff and strong enough to prevent load from entering this roof system. In reality, the framing in a post-frame structure is rarely stiff enough to keep forces out of the roof system. Therefore, areas such as panel endlaps can become overloaded. Symptoms of Endlap Compromise 1. Leaking panel endlaps 2. Endlap and nearby fasteners backing out 3. Holes in the metal panels at the endlaps becoming elongated (both steel and aluminum) 4. Endlap fasteners shearing off just below the washer 5. Endlap fastener washers tearing and separating 6. Wood framing deterioration under the endlap area Common Observations with Endlap Compromise 1. Individual roof panel lengths in applications requiring endlaps tend to be 24’ or less for steel, and 16’8” or less for aluminum. Individual panel lengths longer than these values have a significantly higher frequency of endlap issues. Reducing individual panel lengths below these values does help to reduce endlap issues and has historically been the industry’s suggestion. However, reducing individual panel lengths has not proven effective on these more recent, much larger structures. 2. Roof systems with more than one endlap in an eave to ridge panel run (i.e. three or more panels) have more issues than an application with a single endlap in an eave to ridge panel run (i.e., two-piece roof). Applications with a single panel and no endlaps have few issues, provided the panel length is below 36’ for steel and 20’ for aluminum. 3. Endlap issues tend to be more significant at weaker, more flexible areas of the roof system. Post-frame structures by design have variations in building flexibility/stiffness within the structure. The stronger and stiffer roof areas seem to resist movement better, and force the issue to weaker, less stiff areas. Roof system movement combined with panel expansion and contraction often overload panel endlaps on larger structures. The contribution of each, however, is currently very difficult to determine. 4. With problem endlaps, the top or upslope panel at the endlap is the most likely to experience endlap fastener hole elongation over time. Fastener washers at these endlaps are typically also damaged due to the panel movement under the washer. In some cases, fasteners have fractured. Even if roof system movement from weather-related building design loads is minimized through stronger and stiffer framing, roof system metal panels expand and contract at very different rates than the wood framing underneath. 5. With problem endlaps, the endlap fasteners often are observed to be backing out. Butyl endlap sealant tape is commonly omitted at panel endlaps in post- frame structures. Water and dirt siphon upslope between the endlap panels, creating a visible stain and “dirt line.” If the moisture reaches the shank of the endlap fasteners between the panels, it enters the building, causing the wood around the fastener shank to become wet and weakened, and this moisture eventually causes the wood to deteriorate. This moisture issue reduces the endlap fastener’s structural capacity, promoting fastener backout. Butyl endlap sealant tape needs to be installed in panel endlaps. We can’t just worry about handling the forces involved with the endlap—we must keep the endlap dry. 6. 1½” long roof panel fasteners have fewer issues than 1” long roof panel screws in larger structures. Larger diameter screws also have fewer issues. www. mrca. org — Midwest Roofer 13
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